Efficiency indicating apparatus



Aug. 12, 1941. w E GERMER I 2,252,369

EFFICIENCY INDICATING APPARATUS Fiied March 10, 1939 Attorneys Patented Aug. 12, 1941 OFFICE EFFICIENCY IND-ICATING APPARATUS Wilhelm E. Germer, Berlin-Charlottenburg, Germany Application March 10, 1939, Serial No. 261,027 In Germany August 21, 1937 3 Claims.

This invention relates to efficiency indicating apparatus and more particularly to the indication of the instantaneous emciency of steam boilers or the like.

One of the objects of the invention is to provide an extremely simple and inexpensive means of measuring and indicating boiler efficiency. According to one important feature the efficiency is, measured by combining measurements of two factorsof boiler operation; preferably steam flow and gas flow.

If complete combustion is assumed and the instantaneous total heat energy supplied to the boiler is designated by E, the heat energy carried off by the flue gas by E1, the energy flowing out in the steam by E2, and the heat energy otherwise dissipated by E3.

The factor Eb is made up of losses due to radiation and conductivity and fuel losses in the ashes and soot. These losses are relatively small, from 4% to 6%, and are substantially constant for a given boiler. Therefore, having once been determined for a boiler they may be considered as remaining constant.

In terms of percentage,

wher Va is the flue gas loss in percent, 1 is the percent of heat flowing out in the steam which is a measure of boiler efficiency, and a is the percent of constant losses Reducing the terms E1 and E2 to measurable factors,

where RM is the flue gas flow in M /sec. at

C. and 760 mm. of mercury, Rt is the flue gas As the numerator a is constant the efficiency is proportional to the denominator or the quotient.

The heat capacity of saturated steam changes very little with pressure and changes in heat capacity of superheated steam can be compensated for any changes in steam temperature by errors in indication of about equal value but opposite direction of a steam flow meter of the difierential pressure. type having no temperaturev correction. A constant value in may therefore be used for the heat capacity of the steam where steam flow D is measured by a. diiferential' pressure type flow meter without temperature correction. 7

Assuming also a constant mean feed water temperature tso and designating deviations of the actual temperature from the mean by T,

1Its='i F T is,

=(1 FS.T).(i -ts where S is a constant with the value z ts The flue gas temperature affects both the flue gas measurement and the factor Rt-t. The correction factor of the temperature on the indication of a flow meter of the differential.

type is where Rto is the constant mean temperature for which the meter has been calculated and At is the deviation of the actual flue gas temperature from Rto. From this As the values and are very small, one can set approximately With e When X RM(1 i MAt) Thus eificiency is proportional to a function of X which contains four measurable variables, RM, D, At and T. This method as so far described and suitable apparatus for carrying it out are more fully disclosed and claimed in my copending application Serial No. 228,711, filed September 6, 1938.

Determination of the efficiency can be simplified by assuming a constant mean feed water temperature. This is permissible since changes in feed water temperature are small and have only a small effect on the results.

I have found that the flue gas temperature for a given boiler is a function of the steam flow as long as the boiler condition, that is the cleanliness of the boiler, can be considered as constant. The relation between flue gas temperature and steam flow can be determined by measurement for a given boiler and can be plotted in the form of a curve from which flue gas temperature can be determined for any rate of flow. Thus, according to the present invention instantaneous boiler efficiency can b obtained by measuring only gas flow and steam flow and combining these measurements according to the the quotient X. f

The correct relation between the quotient RM:D or DzRM, continually determined by a quotient meter, and the corresponding value of the boiler efliciency or the necessary scale divisions, may also be obtained by the following method.

Assuming again a complete combustion within the boiler the determination of the instantaneous efficiency 1 and the instantaneous flue gas loss Va can also be obtained in the following manner. It is known that the supplied amount of fuel B in kg./sec. is proportional to the product of flue gas flow RM times its percentage of CO2 or proportional to the product of RM times its (21O2) percentage. The influence of the humidity can be considered here by a factor F,

' the influence of the fuel loss in ashes and soot by a factor 8 and the influence of the kind of the fuel can be considered by a factor b, as all these influences change the flue gas flow for given conditions. If Hu signifies the lower heating value of the combustible in kcal. per kg. of fuel, the fuel energy E can be expressed in the following manner:

With this the apparent eficiency 1 can be obtained:

The measurement of the generating heat (z'ts) can be carried. through in the same manner as in the above described method. A determination of i is not required, if the steam flow is measured by a flow meter of differential pressure type without temperature correction. It is sufficient to observe the changes in feed water temperature. In a similar manner the apparent flue gas loss is determined by:

The so determined apparent values for the boiler efficiency 7; and flue gas loss Va in percentage are not completely accurate, however, as the 002- or Oz-percentage cannot be obtained as an exact representative value of the total flue gas flow, and as the composition and the lower heating value change-continually even for the same fuel.

A principal error of such a determination of 1 or Va has its origin in the sole consideration of the supplied instantaneous fuel energy, while the action of the heat capacity of the boiler, which influences the steam generation, is not taken into account at changes in load. On the other hand, the values for 7; and Va can be utilized to calculate the correct values n and Va. Any error in and Va will be because the sum of 1 and Va plus the constant loss a varies from the figure 100. As all errors and other unknown sources influence the result of the measurement for 11' and Va in similar straight proportional manner and as 1; Va 100 a one can set up the proportional relation:

n+ Va n-l- Va 100a Herefrom one obtains:

100 a 1 mt and similarly l00 Va= g,-Va

The determination of the instantaneous efliciency or correspondingly the instantaneous fiue gas loss requires, therefore, thedetermination of the apparent values for efficiency and flue gas loss by measurement of the flue gas flow RM, the CO2- or Oz-percentage, the steam flow and the generating heat (i-ts) of the steam, it being assumed that the values for the combustible used are known. The determined apparent values for efiiciency and flue gas loss have then to be corrected'by the factor Similarly one obtains:

Suitable apparatus for carrying out the inverition is illustrated. in the accompanying drawing, in which:

Figure 1 is a diagrammatic view of a boiler having an indicating system embodying the invention;

Figure 2 is a partial diagram of a modified system; and

Figure 3 is a partial view of an instrument for indicating a correction due to changes in boiler conditions.

In Figure 1 there is shown a boiler Ill having a stoker I2 or other suitable fuel feeding means and an air inlet passage l4 and a flue l6 connected to a suitable stack or the like. A series of tubes 18 are arranged in the boiler and are connected to a steam drum 20 from which a pipe 22 leads to any desired steam consuming devices.

In order to measure the fiow of gas from the boiler a venturi 24 is placed in the flue l6 and a gas flowmeter 26 is connected by pipes 28 to points at the entrance side of and at the throat of the venturi. The flowmeter 26 operates a cam 30, turning it to different positions as the flow varies.

Steam flow is measured by placing an orifice plate 32 in the pipe 22 and connecting its 0ppo site sides through lines 34 to two flowmeters 36 which turn cams 38 and 40 respectively and which are not corrected for temperature changes.

The steam flow and gas flow measurements are combined according to the above formula by pro: viding rollers engaging the cams 3D, 38 and 40 which control springs 42, 44 and 46 acting on a lever 48 pivoted substantially at its center. A spring 50 abutting an adjusting screw 52 is preferably provided which may be adjusted to take care of the constant losses and other constant factors.

In solving for the quotient X the cam 30 is shaped to give the spring 42 a compression force proportional to the logarithm of the gas flow RM. The cam 40 is shaped according to the logarithm of the quantity liMAt modified by the relation between gas temperature and steam flow. Since springs 42 'and 46 act in the same 7 direction these forces will be added to produce a force proportional to the product RM (lztMAt) This force is balanced against the force of springs 44 and 50, the former being proportional to the logarithm of the steam flow D and the latter being adjusted to compensate for the constant factors including specific heat of the steam and feed water temperature. Thus the lever 48 willtake a position dependent upon the value of the quotient X and may carry a pointer 54 reading efiiciency directly upon a suitable calibrated scale 56.

Figure 2 illustrates a modified construction, parts therein corresponding to like parts in Figure 1 being indicated by the same reference numerals plus Hill. This construction is substantially the same as that of Figure 1 except that the second steam flow meter is omitted and the cam I38 is shaped to perform the functions of both cams 38 and 40 of Figure 1. That is, a single steam flow meter operating a single cam performs the functions of the two meters of Figure 1 and exerts the same force on the lever I48.

The above-described methods are correct only for a constant boiler condition. As this change is not visible from the outside of the boiler the methods contain an uncertainty in the adopted fixed relation between flue gas temperature and steam flow. A change in boiler condition, as occurs for instance, if the boiler gets dirty, decreases the value of'D at the same boiler operation and increases the flue gas temperature Rt considerably, while the flue gas flow RM remains unchanged.

For this kind of boiler operation, which assumes a constant boiler condition and a fixed relation between steam flow and flue gas temperature, a visible indication of a change in boiler condition is necessary for completely accurate results. For this purpose a single measurement of the flue gas temperature Rt may be used.

In the original condition of the boiler a definite boiler load or steam flow rate results in a definite flue gas temperature. To carry out the correction for boiler condition a convenient testing load D, for instance 60% of the boiler capacity is chosen and the flue gas temperature Rt for that load is determined. Upon a change in boiler condition resulting in a change in efficiency the temperature Rt will vary for the same load D.

If u designates the absolute size of this change of the boiler eificiency 7 it will drop to (1 u) or 7; for a dirty boiler. The changes in energy AE for the generation of steam at the testing load D will have the value of:

This must equal the change AE or increase in energy of the latent heat contained in the flue gases:

if MRI) represents the change of the flue gas temperature Rt in degrees centigrade, due to a change in boiler condition and RM the flue gas flow corresponding originally to the testing load D. As both changes in energy are equal, the change of the flue gas temperature can be determined at once for any given change :11. of the boiler efliciency 1;. One gets for a changed efficiency of (v; Fu):

V This equation furnishes at once a definite scale for any poorer or better condition of the boiler in percentage. One has only to insert for u the values 1, 2, 3, per cent and so on and to calculate, the respective difference in temperature.

For a flue thermometer scale starting on the left side and reading from left to right this will give for increasing temperatures of Rt a percentage scale to the right for poorer boiler conditions and for decreasing temperatures of Rt a percentage scale to the left for better boiler conditions than before.

One suitable instrument for indicating the correction is illustrated in Figure 3. As shown this instrument comprises an upper scale graduated in degrees centigrade of gas temperature and. a lower scale graduated in and efflciency. The lower scale is so located with respect to the upper scale that its zero point coincides with the test temperature Rt.

Apointer 80 is moved across the scales by any desired mechanism, not shown, in response to variations in the fiue gas temperature.

The relationship of the scales may first be established by measuring the flue gas temperature Rt and the flue gas flow RM at the selected test value of D, say 60% of the boiler rating. Thereafter to determine the effect of changes in boiler condition the boiler may again be adjusted to the values of D and RM. At

the test values RM and D slightly more fuel may be required to' maintain the steam flow D than originally due to a slight decrease in efficiency as the boiler becomes dirty. This will change slightly the amount of excess air and will tend to increase the flue gas temperature. However, the decrease in excess air is so small and has such a small effect upon flue gas temperature that its eifect may be disregarded and the indicated change in boiler efficiency may be accepted as correct.

One can read then the value and the direction of change in boiler condition easily on the lower percentage scale of the instrument.

While several embodiments of the invention have been described it will be understood that it is not intended to limit the scope of the invention by the above description nor otherwise than by the terms of the appended claims.

What is claimed is:

1. Apparatus for indicating the efliciency of a steam boiler or the like comprising means for measuring the flow of steam from the boiler, means for measuring the flow of gas from the boiler, means operated by said first named means for creating a force proportional to a function of steam flow and a second force proportional to a function of flue gas temperature, means operated by said second named means for creating a force proportional to a function of gas flow, and means for balancing the first named force against the sum of the last two forces to obtain a resultant proportional to boiler efficienoy.

2. Apparatus for indicating the eificienoy of a steam boiler or the like comprising means for measuring the flow of steam from the boiler, means for measuring the flow of gas from the boiler, cams operated by said means respectively, a balance lever, and springs controlled by said cams and urging said lever in opposite directions whereby it will occupy a position dependent upon the ratio of the forces of said springs.

3. Apparatus for indicating the efficiency of a steam boiler or the like comprising a flowmeter responsive to the flow of gas from the boiler, a pair of flowmeters responsive to the flow of steam from the boiler, cams operated by said flowmeters respectively, said cams being shaped to produce movements corresponding respectively to functions of gas flow, steam flow and gas temperature, a balance lever, and resilient means connecting said cams to the balance lever to balance it in a position proportional to boiler efliciency.

WILHELM E. GERMER. 

